In the field of municipal and industrial wastewater disposal, it is necessary to treat the resulting wastewater sludge by heating to reduce the sludge volume by reducing its water content by evaporation and to reduce the sludge borne pathogens and its potential for vector attraction. Moreover, such sludge can contain toxic and/or corrosive components which must be removed in an economic and environmentally safe way. Thermal drying of this sludge has emerged as one of the preferred treatment methods. In many instances, infrared heaters are used as they are the most energy efficient as it results in lower heat losses during the transfer and a substantially smaller air emission control system.
An example of a sludge dryer is described in U.S. Pat. No. 5,974,688. This dryer installation is monitoring and regulating the temperature of the material to be dried and also monitors and regulates the temperature of the dryer itself. The monitoring system allows the material drying efficiency of the dryer to be maximized and at the same time reduces the risk of occurrence of combustion and damage to the dryer and its components due to temperature induced expansion and fatigue.
Another example of a dryer of wastewater, which can also be used to dry sludge, is described in FR 2875721. This system is using infrared radiation to dry a moving amount of wastewater.
U.S. Pat. No. 5,046,944 discloses a gas-fired burner with porous ceramic face through which gaseous combustion mixture emerges and on the emerging surface of which the mixture burns. The gas-fired burner can heat a substrate with help of streams of air or recycled combusted gas which is sweeping across the substrate to help remove moisture or other volatiles from the substrate. The gas-fired burner can be used for heat-treating moving webs carrying volatilizable material that contaminates the atmosphere if merely discharged into the air. U.S. Pat. No. 5,046,944 contains an example where the combustion gas and the volatilized material of the dried web are completely separated by means of a thin sheet of infra-red-transmitting material such as quartz.